One typical group of organosilicon compounds is silane coupling agents. The silane coupling agents have two or more different functional radicals in their molecule, and serve as a chemical bridge to bond an organic material and an inorganic material that would otherwise be difficult to bond. In the silane coupling agent, one functional radical is a hydrolyzable silyl radical which forms a silanol radical in the presence of water. This silanol radical, in turn, reacts with a hydroxyl radical on the surface of inorganic material to form a chemical bond to the inorganic material surface. The other functional radicals include vinyl, epoxy, amino, (meth)acrylic, mercapto and similar radicals which form a chemical bond with organic materials such as various synthetic resins, as well as ureido, isocyanurate and other polar radicals which do not form a chemical bond, but hydrogen bond or otherwise interact due to their polarity. By virtue of these attributes, the silane coupling agents are widely used as modifiers, adhesive aids, and various other additives in organic and inorganic resins.
Among others, those silane coupling agents having non-bonding functional radicals such as ureido and isocyanurate are used as resin modifiers and paint additives. Generally isocyanurate silane coupling agents are advantageous in that their hydrolytic condensates have a film forming ability since they are of tris(silyl) type, and that they are compatible with resins because of inclusion of polar radicals. However, these silane coupling agents find limited use in aqueous applications because of a lack of water solubility.
Heterocyclic structures similar to isocyanurate include triazine structures. Mono(silyl) silane coupling agents having triazine structure are disclosed in JP-A 2006-213677 and JP-A 2007-131556. These patent documents relate to only organosilicon compounds of triazine structure having a thiol radical(s) introduced therein. With such teaching, a melamine skeleton as disclosed herein cannot be formed. On account of the thiol radical being introduced, a tris(silyl) structure as disclosed herein cannot be formed.
JP-A H07-026242 discloses an adhesive composition comprising a silicone-modified melamine resin. Since a melamine resin derivative is tied with silicone by condensation of hydroxyl with silanol, undesirably the modified resin is prone to untying in the presence of water or alcohol. Silane coupling agents are nowhere described. JP-A H11-100237 discloses a composition for use as a glass fiber sizing agent, comprising a melamine resin and a reactive silane coupling agent. Since this material is a blend of components, it is impossible to isolate the material as a compound and identify the structure thereof.